Effects of exogenous growth hormone and diethylstilbestrol on growth and carcass composition of growing lambs.

An 8-wk growth trial was conducted to assess the effects of ovine growth hormone (oGH; 7 mg/d, sc) on growth performance and carcass composition of normal, growing wether lambs. Diethylstilbestrol (DES; .1 mg/d, sc) and control lambs were included for comparisons. Plasma oGH levels at 8 wk were 1.9, 5.5 (P less than .05) and 138.1 ng/ml (P less than .001) for controls, DES and oGH lambs, respectively. Diethylstilbestrol did not increase plasma oGH until the fourth week. The oGH improved feed conversion 7.4% (FC; P less than .05), but did not alter average daily gain (ADG) or feed intake (ADF). Diethylstilbestrol increased ADG 15.3% (P less than .05) and improved FC 16.1% (P less than .01), with no effect on ADF. The primary effect of oGH on carcass composition was to decrease the quantity of fat 8.9% (P less than .05). In addition, oGH may have increased protein 6.5% (P less than .10) and moisture 4.0% (not significant). Diethylstilbestrol increased the quantity of carcass protein 10% (P less than .01) and moisture 8.7% (P less than .05), with no effect on fat. In these studies, the primary effect of exogenous oGH on normal, growing lambs was to reduce carcass fat, which may account for the observed improvement in FC. Diethylstilbestrol, at 1/70th of the oGH dose, was superior to oGH for improving FC (P less than .05) and ADG (P less than .10). Improvements in body weight of the lambs given DES were observed 2 wk before an increase in plasma oGH. In addition, DES, unlike exogenous oGH, did not alter the quantity of carcass fat. These observations do not support the concept that the mode of action of DES is through increased GH secretion.